chrome/browser/resources/media_router/extension/concat_js_modules.py

# Copyright 2018 The Chromium Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.

"""This script concatenates JS files into a set of output files.

Modules are specified as a list of strings of the form
module=<name>:<num>[:...], where <name> is the name of the module and
<num> is the number of JS files that should be concatenates to make
the module file, and if a second : is present, everything after it is
ignored.  (This strange format is used because it is compatible with
JSCompiler's --module flag.)
"""

import argparse
import os.path
import re

def main():
  parser = argparse.ArgumentParser()
  parser.add_argument(
      "--module-specs", nargs="+",
      help="List of module specifiations.")
  parser.add_argument(
      "--output-dir",
      help="Directory where output files are written.")
  parser.add_argument(
      "sources", nargs="+",
      help="JS input files.")
  args = parser.parse_args()

  # Loop over all specified modules, and simulaneously traverse the
  # list of source files using `source_index`.
  source_index = 0
  for spec in args.module_specs:
    # Split the module spec into a module name and a count of source
    # files to include in the module.
    pre, sep, post = spec.partition("module=")
    assert pre == ""
    assert sep
    parts = post.split(":")
    module_name = parts[0]
    input_count = int(parts[1])

    # Write the module file.
    module_file = os.path.join(args.output_dir, module_name + ".js")
    with open(module_file, "w") as module_out:
      # Append as many input files as requested by the module spec.
      for i in range(input_count):
        source_file = args.sources[source_index]
        source_index += 1
        module_name = None
        with open(source_file, "r") as source_in:
          module_out.write("goog.scope(() => {\n")
          # Copy input line by line.
          for line in source_in:
            m = re.match(r"goog\.module\('([^']+)'\);\n", line)
            if m:
              # Handle goog.module statements specially.
              module_name = m.group(1)
              module_out.write("let exports = {};\n")
            else:
              # Typical case: just copy the line verbatim.
              module_out.write(line)
          if module_name:
            # Put exported names into the global namespace.  That's
            # not now goog.module is supposed to work, but it's close
            # enough.
            module_out.write(
                "__setGlobal('{}', exports);\n".format(module_name));
          module_out.write("});\n")

  # Check that every source file has been appended to a module.
  if source_index != len(args.sources):
    sys.exit("Too many input files.")

main()